Hitherto, many systems of remote controlling which employ bursts of single frequency wave, the number of bursts being preset, are known. For instance, a transmitter comprises buttons for operating switches for causing the transmitter to transmit various kinds of train of ultrasonic waves from its speaker to a receiver. In a widely used example, by pressing a first button, a first kind of train consisting of two bursts of ultrasonic wave is produced, by pressing a second button, a second kind of train consisting of three bursts of ultrasonic wave is produced, and so on. In the receiver, upon receiving abovementioned various kinds of the ultrasonic wave bursts, by decoding the wave bursts to develop to a count, several kinds of outputs are obtainable at its several output terminals. Accordingly, corresponding to the buttons of the transmitter, several kinds of controls, for instance, ON-OFF of power switch, channel selection and sound-volume control can be made.
In another conventional system, a little more sophisticated mechanism has been devised. Namely, binary-coding is utilized for several control items, and according to the binary-coding, a pulse code modulation is made in arranging the bursts of the ultrasonic waves of a single frequency.
However, the abovementioned remote control systems utilizing ultrasonic waves of a single frequency are likely to be disrupted by external ultrasonic noises from rattling of a bunch of keys, telephone bell, etc., or by fluorescent lamp light in case of light transmission system. Namely, when such noises containing components of the ultrasonic signal or the light used and the noises continue for a specified period to be detected by the decoder in the receiver, then the components of the noises form spurious pulse and are erroneously detected in the receiver, thereby causing the counter to malfunction.